The operation of a mine hoist in moving skips and cages vertically up and down within the hoist shaft is of great importance in the necessary movement of workers and mined product from underground.
The cost of excavating a deep shaft, and providing the necessary shaft guides within the hoistway, together with the cost of providing and operating the winding machinery and cable is such that efficient high speed hoisting plays an important role in the economic operation of the mine.
Mine shafts may extend vertically several thousand feet into the earth, such as 8,000 feet deep and safe, rapid hauling is of great importance.
Wooden or steel guides in aligned vertical relation, supported from the shaft timberwork, serve to provide guidance for the cage or skip in its passage up and down the shaft. These guides are subject to displacement and misalignment from earth settlement, and from general wear and tear, including the reactions generated by impacts from guide skids and guide rollers of the cages passing up and down.
At winding speeds in excess of fifteen hundred feet a minute the impacts resulting from misaligned guides can produce savage lateral displacement forces acting on the cage, the cable and by rope whip winding machinery, as well as the shaft guides. It should be born in mind that personnel also are transported by the system.
The stability of the cage in its passage up and down the hoistway is further influenced by the polar twisting torque of the hoisting cable, which torque is not constant but may have a considerable range of variation as the conveyance moves in the shaft.
Many systems of guide rollers have been tried in the mining industry, with varying degrees of success. However, the prior art hoist stabilizing systems have been incapable of providing adequate stability in guiding skips and cages to meet modern requirement in terms of hoisting speeds, increased tonnages and reliability.
Turning to the prior art, the guidance system disclosed in U.S. Pat. No. 4,434,876, utilizes a two-direction, two roll arrangement wherein the lateral displacement of each guide roll as it travels up and down a respective surface of a guide rail, is controlled by two coil springs. The two springs are connected in series, such that lateral displacement of the guide roll compresses both of the springs. The softer first spring operates within a protective yoke which limits the extent of total compression. Continued roll displacement is accommodated by further compression of the second, stiffer spring. Thus a progressive, two rate spring is provided.
The elements comprising the arrangement are poorly protected for operation in the damp, hostile and frequently corrosive environment of a mine shaft.
Certain prior art elevator roller guide arrangements, while being totally unsuited to use in mine shaft environments, understandably contain some elements in common with the present invention.
U.S. Pat. No. 3,099,344 Tucker, July 1963 shows an elevator roller guide arrangement having a pair of opposed guide rolls in facing relation to contact the sides of the guide rail, and a third roll at right angles thereto, bearing on the inner edge of the guide rail.
The pair of opposed guide rolls are mechanically tied together for synchronized lateral displacement, having centering springs, the actions of which are moderated by oil filled dashposts.
U.S. Pat. No. 2,260,922 Spiro, October 1941 shows an elevator car guide arrangement having sets of double-wheel bogies contacting the sides and inner edge of the guide rail. Each bogie comprises a centrally pivotted beam, the central pivots of which are supported by hydraulic cylinder to resiliently load the beam supported guide rolls against the respective beam surface. A common pressure source keeps the beams and the guide rolls uniformly loaded in balanced relation against the guide rail. However there appears to be no centering bias forces to keep the system centred and stable.
Both systems are inadequate and entirely unsuited to the environment of a mine shaft, and to meet the requirements of high hoisting speeds.
German Auslegeschrift 1067195 Abt, October 1959 is directed to guides for a mine cage, utilizing inclined rubber springs which can be preloaded and laterally displaced into position. The roll repositioning provisions are quite elaborate. This complex guide arrangement operates the main rubber "springs" in both shear and compression, and must be adjusted empirically for a desired load range.